N-doped graphene nanosheets-based optical nano switch for the selective detection of guanine and Pb2+

The development of biosensors for the selective detection of Pb2+ and guanine is critical for the elucidation of lead toxicity and human health monitoring. In this research, blue-green luminous water-soluble nitrogen-doped graphene nanosheets (ws-NGNSs) were synthesized from biomass as an optical sensor for guanine and Pb2+ in aqueous media. A facile hydrothermal approach followed by mild oxidation was used for the synthesis of ws-NGNSs, where rotten pear was used as the carbon source and urea was used as the nitrogen source. The ws-NGNSs emitted intense fluorescence at a maximum excitation/emission wavelength of 340/425 nm. The addition of Pb2+ effectively quenched the blue-green emission of ws-NGNSs with prominent selectivity. The selectivity is attributed to the synergic effects of heteroatom doping, surface functional groups, and surface-active sites. Further, ws-NGNSs/Pb2+ was used as a promising fluorescent probe for the selective recognition of guanine. The addition of guanine induced the fluorescence “turn on” effect. Therefore, ws-NGNSs with excellent fluorescence properties can be used as efficient fluorescence “on-off-on” nano-switches for the selective detection and differentiation of Pb2+ and guanine with limits of detection of 8 μM and 0.2 μM, respectively. The possible sensing mechanism is explained using fluorescence and UV-vis spectroscopy. Water-soluble NGNSs have a solid foundation for the fabrication of optical sensors for biomedical and environmental applications.